The overall purpose of this project is to understand the molecular mechanisms responsible for the maintenance of cell shape and volume as well as dynamic activities such as cell motility. This knowledge should be useful in understanding the mechanism by which white cells can move to sites of injury and phagocytose foreign material as well as the pathophysiology of phenomena such as cell injury and cell swelling. It is thought by most workers in the field that many if not all of these properties are mediated by the cytoskeleton which is found in the peripheral cytoplasm. F-actin is a principal component of this structure, and in addition there are a number of other proteins which can modulate actin properties. It is the purpose of this project to elucidate these cell processes by understanding the mechanical properties in simple shear and in bulk deformation of F-actin alone and in combination with these actin modulating proteins. The conditions which will be examined are the effect of length, concentration, and crosslinking on the dynamic moduli, G' and G" over a wide range of frequencies and shear stresses. The effect of a number of crosslinking proteins on the rheologic behavior of F-actin will be compared. In particular the differences between high molecular weight actin binding proteins obtained from rabbit pulmonary macrophage, rabbit smooth muscle, chicken smooth muscle, and toad eggs as well as alpha-actinin will be measured. The mechanical measurements will be correlated with morphologic information obtained from electron microscopy. This data will be used to derive empirical relationships between the rheologic parameters and length, concentration and degree of crosslinking. A theoretical description of the system will be made in order to predict the experimental rheologic parameters. The interaction of F-actin systems with water will be explored by determining their response to isotropic forces. In particular the mechanism by which F-actin systems can swell or shrink in response to an osmotic or hydrostatic force will be determined. This information should be useful in the interpretation of data obtained from whole cells.